This invention relates to a power lever apparatus through which a control member schedules fuel to operate a turbine engine.
Controls for gas turbine engines should not require the operator to use special precautions in his movement or positioning of the power request input during engine operation. During primary control operation, several engine parameters such as speed, compressor pressure, air temperature, turbine temperature, etc. are normally sensed and used to compute the level and rate of change of fuel flow and variable geometry position so as to prevent engine overspeed and/or overtemperature, and avoid engine stall during acceleration/deceleration of engine speed. Such primary control system complexity is well understood by those familiar with this art, and is typical of the majority of gas turbine engine controls in use at the present time.
In many cases, such as a single engine aircraft, a backup control is required to operate the engine in the event of failure of the primary control system. To keep cost and weight to a minimum, it is desired that the backup control be as simple as possible, and the number of engine parameters sensed be minimal, such as air temperature and pressure. To maintain simplicity in current practice, the fuel flow and variable geometry are scheduled directly as a function of power lever input by the operator, which restricts the operator to the rate and position of the power lever during operation, such as disclosed in U.S. Pat. No. 4,245,462 McCombs, filed Nov. 29, 1978, where the input from an operator as applied to the power lever is directly transmitted to the operational fuel control. Each turbine engine must operate within an aircraft flight envelope without causing turbine overtemperature and/or engine overspeed. Due to the entire flight envelope, the maximum input is such that fuel flow may be unnecessarily restricted in certain areas of the flight enevelope. Thus, even though the power lever position is at maximum power, the gas generator may be operating at a thrust level below the capacity of the turbine engine. In situations wherein the turbine eingine is in an aircraft, for take-off it is important that the turbine engine operate at its maximum thrust capacity.